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sliding eastward underneath the continental plate of North America. This eight-hundred-mile (1,300 km) fault, the boundary line between two tectonic plates, will later be named the Cascadia Subduction Zone. As I listened to John Adams, it sounded exactly like Dieter Weichert’s description of the plate that got stuck sliding underneath Mexico. Until September 19, both fault systems had been thought of as aseismic.

    I didn’t know it at the time, but John Adams had already been studying this mystery for five years. He had published three papers on faults that lie deceptively silent for hundreds of years, including an alpine fracture zone in his home country of New Zealand. Now, in one long breath, he had just warned us that what we saw in Mexico City might also happen in the Pacific Northwest. And Adams wasn’t the only one to say it.
    Garry Rogers was the young PGC seismologist whose job it was to monitor the two hundred or so temblors that rattle through southwestern British Columbia every year (only two or three of which are strong enough to be felt). He told us the historical lack of huge megathrust events off the west coast of Vancouver Island could be very misleading.
    â€œThe implication,” said Rogers with focused intensity, “is that the possibility for very large earthquakes—the kind that occurred in Mexico just recently—does exist on the west coast of Canada. The problem is that in the 150 short years that we’ve been here, we have not seen any examples of earthquakes on our subduction zone. Not even small ones.”
    He explained that those two hundred rumbles occur because of stress within the overlying crustal plate, relatively close to the surface. The much larger shock—if it does happen—would occur almost forty miles (65 km) below ground along the length of the subduction zone. Like Adams, Garry Rogers thought the absence of deep Juan de Fuca quakes put seismologists in a quandary.
    â€œAt the moment, we just don’t know,” he said. “It’s a subject of scientific debate. But if we compare other areas around the world that are very similar to our subduction zone, we find that we are the only one that has not had large earthquakes.”
    For seismologists in 1985 it was hard to imagine why the Juan de Fuca plate (or the Cocos plate in Mexico) would be special—the only place on the planet where two plates glide past each other trouble free. How could this not be like the dangerous and deadly subduction faults off the coasts of Alaska, Chile, and Japan? Although Rogers didn’t seem like a gambler, he was willing to speculate.

    â€œA more likely scenario, comparing it with other zones, is that we are capable of large earthquakes but with very long intervals in between them,” he said. The long quiet history of Juan de Fuca could mean “it’s stuck and one of these days we’re gonna have a monster earthquake like Mexico had.”
    If the fault were “stuck,” I wondered, could the build-up be measured and—if you could see the stress increasing—would it be possible to predict the next quake? “It may be,” answered Rogers. “And, in fact, one rather suspects it should be, because before such a large earthquake a tremendous amount of strain is stored up. We might be able to detect a deformation like that. In fact, they can see this kind of thing in Japan since their last big earthquake—deformation going on.”
    Evidently rocks bend and tilt under stress and there are changes in electrical signals coming from the earth, all of which could be monitored. Rogers described prediction as a dark art that was still many years away from success, but his point was that there are things we could and should be doing to confirm or deny the possibility of large subduction earthquakes off the Pacific Northwest coast.
    It turned out that John Adams was already doing exactly that kind of research. Less